Rear Axle Oil – Silvery Discolouration of the Lubricant
Whilst changing the rear axle oil on Volvo FH and FM trucks technicians may sometimes discover a silvery discolouration of the lubricant. This is particularly the case with FH and FM Volvo trucks up to 2001 fitted with the RS1344 range of differentials and Volvo FH and FM trucks aged 2002 onwards which are using the RSS1344B Diff. It is highly recommended that if there’s any evidence of the gear oil having a silver tinge further investigation should be taken without delay in order to avert a possible catastrophic failure of the differential.
This post highlights the common causes of this silvery looking contamination of the rear axle oil before suggesting ways in which this common problem can be successfully resolved.
During our time working on Volvo FH and FM trucks we’ve found the most common cause of the contamination of the lubricant to be the disintegration of the sun gear thrust washers inside the differential unit, which if caught at an early stage may well be repairable to a satisfactory standard by simply replacing the thrust washers.
Volvo OE ( 3152160 )
|Thrust Washer Kit |
Volvo OE ( 8171096 )
VTP number 270082
For the earlier RS1344 differential the correct thrust washers are Volvo OE part number ( 3152160 ) which is our VTP part number 207944. However if the vehicle is fitted with the later RSS1344B differential then a thrust washer kit would be required. This thrust washer kit is Volvo OE number (8171096 ) and VTP number 270082.
Any delay in taking appropriate action could easily allow running tolerances to fall outside of the manufacturer specifications, potentially allowing the axial forces to throw the sun gears outwards often resulting in the failure of the gears when under high stress. This type of failure commonly causes a tooth to break off resulting in the rapid breakup of the gear train, which in turn often causes the differential to lock up, this being diagnosed by a loud banging noise from the rear axle when the truck is turning.
|Sun and Planet |
Gear Repair Kit,
Volvo OE ( 85100855 )
Once the Differential begins to show the symptoms of locking up there are two options for repair; either replacement with an appropriate unit of the correct ratio or repairing your own unit by removing the crown wheel assembly from the differential carrier and splitting the differential housings to fully assess the extent of the damage. If the housings aren’t too badly damaged then you can make a cost-effective repair by fitting a sun and planet gear repair kit, Volvo OE part number 85100855 which converts to VTP part number 207769. However you must ensure you re-assemble the differential unit exactly as per manufacturer’s specifications.
|Differential Housing |
If the loose pieces of broken gears have been grinding away inside the carrier housing the differential housing may have suffered excessive damage meaning that the housing will also need to be replaced, this replacement will require VTP part number 270037.
On occasion, having suffered the damage previously described, the sun gear may split which can then result in the half shaft jumping over the splines when put under torque subsequently damaging the half shafts. The splined half-shafts can be replaced from our stock depending on which type are fitted. On RSS1344B axles using single spline half shafts you need VTP part number 70043 (OE 8172096) for double spline half-shaft use VTP part number 70044 (OE 8172097).
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